STUDIES ON THE PLASTICITY OF DORMANCY AND ON AGING IN SWITCHGRASS SEEDS

Degree:

Doctor of Philosophy

Department:

Crop and Soil Environmental Sciences

Committee Chair:

David J. Parrish

Chair's email:

davp@vtvm1

Committee Members:

Azenegashe O. Abaye

David Orcutt

Gregory E. Welbaum

Dake D. Wolf

Keywords:

seeds, switchgrass, panicum virgatum, dormancy, aging

Date of defense:

July 02, 1997

Availability:

Release the entire work for Virginia Tech access only.
After one year release worldwide only with written permission of the student and the advisory committee chair.

Abstract:

The dormancy of switchgrass (Panicum virgatum L.) seeds may be broken by a
variety of treatments, including after-ripening and stratification.
This study was conducted to investigate and characterize more systematically
factors affecting both after-ripening and stratification effectiveness, and
the aging that can occur concomitantly with after-ripening. More than one
year of after-ripening at ambient temperature and humidity was necessary
for germination of newly harvested seeds to increase from as low as 5% to
around 80%. After-ripening was not accelerated at temperatures above ambient
for seeds stored in paper bags, which permitted the loss of seed moisture at
the increased temperatures. Both after-ripening and aging accelerated with
increases in temperature (5 to 60 °C) and seed moisture content (50 to 130
g kg-1), except that there was evidence of a moisture optimum for
after-ripening that shifted downward as temperature increased. For many seedlots,
storage at 60 °C and 50 g kg-1 seed moisture content for about
1 mo broke most of the dormancy and resulted in acceptably low numbers of
abnormal (aged) seedlings. Decreases in germinability caused by
post-stratification drying of switchgrass seeds (described herein as "reversion",
in which the reverted seeds could be made germinable again by further stratification) increased as the desiccation
increased. Revertibility decreased as stratification or after-ripening time
increased. Stratification and after-ripening worked additively to release
switchgrass seeds from dormancy. Reversion (germination with stratification
minus germination after stratification followed by drying) may reveal seedlot
differences and changes over time and moisture content that can not be seen
otherwise. Imbibed, dormant seeds placed at 21 or 30 °C were induced into deeper
dormancy, as indicated by length of stratification needed to break the dormancy.
Dormancy deepened more as storage temperature and time increased for imbibed
seeds. There are transitional temperature and seed moisture ranges where
opposing processes (aging vs. after-ripening, stratification vs. dormancy
deepening) appeared to overlap or surpass one another. Switchgrass seeds,
either on a single seed level, or on the population level, responded continuously
to changing temperature and moisture conditions. Less aging was observed
for switchgrass seeds stored in N2. After-ripening of switchgrass seemed
not to be influenced by N2 or air. In sum, switchgrass is revealed to be
remarkably plastic in its ability to move toward both greater germinability
and greater dormancy.

List of Attached Files

At the author's request, all materials (PDF files, images, etc.) associated with this ETD are accessible from the Virginia Tech network only.

The author grants to Virginia Tech
or its agents the right to archive and display their
thesis or dissertation in whole or in part in the University Libraries
in all forms of media, now or hereafter known. The author retains all
proprietary rights, such as patent rights. The author also retains
the right to use in future works (such as articles or books) all or
part of this thesis or dissertation.